In a toroidal continuously variable transmission, power rollers are supported by trunnions as disclosed for example by Tokkai Sho 57-47060 published by the Japanese Patent Office in 1982. A piston is fixed to these trunnions respectively. When a piston is driven hydraulically and the trunnions are displaced at right angles to a rotation shaft of an input disk and output disk, the gyration angle of the power roller varies, and a rotation ratio (drive ratio) of the input disk and output disk holding the power rollers varies.
The upper ends and lower ends of these trunnions are respectively fitted to a link so that they can displace in synchronism. Each trunnion is joined to the link via a needle bearing and a spherical joint so as to permit it to rotate freely and incline through a very small range.
When the power roller is inclined, a load acts on the trunnion in a direction other than the anal direction.
This load is absorbed by the relative displacement of the spherical joint and a link. Since there is a small clearance between the needle bearing and the trunnion and between the needles, some needles may incline relative to the trunnion in this case. The inclined needles, however, exert an axial force on the trunnion when it rotates. According to an analysis, about 10% of the force of a radial load supported by the needle bearing acts on the trunnion in the axial direction.
As a result, there is an excess or deficiency of the drive force exerted by the piston on the trunnion, and this results in scatter of torque transmitted by the power rollers.